Vibro compaction vs piling - to shake or not to shake

It is becoming increasingly common to use vibratory techniques, during construction, to improve the load bearing capacity of the ground in preparation for foundations.

With vibratory ground improvement a cheaper alternative to traditional methods such as piling, it’s no surprise it’s becoming so popular!

So what does vibro compaction involve and what are the potential limitations that need to be taken into account before changing the way you provide support for your structures?

Let’s start with the basics.

What is ‘Vibratory Ground Improvement’?

Vibro ground improvement strengthens the load bearing capacities of weak or filled soils to provide adequate support for foundations.

How does it work?

This is done by lowering large high powered vibrating probes from a specially designed rig into the targeted ground. The ground is then back filled with highly compacted aggregate or soil, causing the configuration of the ground to become denser thus making the soil more stable.

Wait… here’s the important bit!

What foundations can be used with vibro compaction?

Vibro compaction on its own is not substantial due to the localised nature of the process and the different soil types. Therefore, it needs to be supported by reinforced foundations which should be:

Either reinforced concrete strip foundations, or a raft/semi raft foundation

Designed by a structural engineer and comply with the minimum requirements for areas of reinforcement as defined by BS 8110

Include suspended ground floors

Where the treated ground comprises cohesive soils, measures must be taken to mitigate the potential effects of vegetation (i.e. subsidence or heave). Refer to Section 5.2 of our Technical Manualfor further guidance

So which is better vibro compaction or traditional piling? Let’s compare the two methods.

Vibratory Ground Improvement vs Piling

To the untrained eye the stone columns left by vibro compaction can be mistaken for piles. However, these stone columns derive their strength from the surrounding soil as opposed to piles which are more than 10 times stiffer than stone columns.

That’s 1-0 to piling! So why would you choose vibro compaction over piling?

Benefits of vibro compaction

It is much quicker than piling and follow-on works can be started straight away

It is cheaper than piling

It provides a flexible option for different types of soils

It is one of the most sustainable techniques and thus the most environmentally friendly

It decreases the chances of liquefaction

Limitations of vibro compaction

It does not work with all soil types so an extensive analysis into the soil should be carried out which is not required for piling

It requires specialist equipment and expertise which would need to be contracted in.

Certain types of vibratory techniques are unsuitable for contaminated land for example when water jets are used as they may spread the contamination further